NERD: A Nanoscopic Humidity Sensor Built Using Graphene Quantum Dots and Bacterial Spores

While the age of robots is still very much prevalent, one can nevertheless discern a slow, yet unmistakable rise of another, quite related field of interest. By combining the intuitiveness of living organisms with the versatility of robots, researchers, across the world, are trying to develop highly-advanced biological machinery. As part of a recent study on bio-robotics and nanotechnology, scientists working at the University of Illinois, Chicago, have created a incredibly futuristic electromechanical contraption, called NERD. Built using graphene quantum dots (GQDs) and a single microscopic bacterial spore, this nanobot actually functions as a humidity sensor.

Graphene quantum dots are nanoscopic crystals of graphene; first isolated from coal, in 2013, by a team of Rice University scientists. Known for their prominent quantum mechanical properties, these crystals could potentially be used in light-emitting diodes (LEDs), solar cells and even transistors. With the development of more efficient manufacturing techniques, the GQDs have become more precious to scientists than ever before. The NERD, actually Nano-Electro-Robotic Device, is a high-tech hybrid gadget operating as a humidity sensor. Vikas Berry, a professor at the UIC Department of Chemical Engineering and the chief author of the study, said:

This is a fascinating device. Here we have a biological entity. We’ve made the sensor on the surface of these spores, with the spore a very active complement to this device. The biological complement is actually working towards responding to stimuli and providing information.

Recently published in the online version Scientific Reports, of the Nature journal, the research explicates the working principles behind the device. Central to the “robotic germ” is a bacterial spore, which is in turn covered with nano-sized graphene quantum dots. Two electrodes are secured on each side of the spore. According to the team, a drop in the surrounding atmospheric humidity actually causes the spore to shrink in size. Consequently, the GQDs, on the spore’s surface, come closer to each other. This step enhances the conductivity of the crystals, as evident from the readings of the electrodes.

The findings show that the sensor is 10 times faster than traditional varieties containing water-absorbing polymers. Unlike the latter, the NERD exhibits improved sensitivity in case of acute low-humidity and low-pressure conditions. What is more, it can provide a reading even in vacuum, making it a valuable addition to spacecrafts where any change in humidity could indicate a leak. Berry was reported saying:

We’ve taken a spore from a bacteria, and put graphene quantum dots on its surface – then attached two electrodes on either side of the spore. Then we can change the humidity around the spore. We get a very clean response – a very sharp change the moment we change humidity. We can go all the way down to a vacuum and see a response. It’s also important in space applications, where any change in humidity could signal a leak.

The research was conducted with partial funding from the National Science Foundation.